When it comes to supporting candidates for public office, the Associated General Contractors of America gives 90 percent of its campaign contributions to Republicans.

And then there is Senator Joseph I. Lieberman.

The group, which represents the construction industry, wrote a $4,000 check last month to Mr. Lieberman, the Connecticut Democrat who is facing a spirited challenge for his party’s nomination from a political novice, Ned Lamont. The money was just a sliver of the $260,000 he has collected from political action committees since March.

But that donation and others like it have fed a perception, stoked by the Lamont campaign and its supporters on the Internet, that Mr. Lieberman is too cozy with Republicans. It is a vexing assertion for Mr. Lieberman, whose centrist politics and pragmatic style, once a source of pride, are now being held against him by liberals and antiwar Democrats.

He is drawing financial support, not unexpectedly, from interest groups that typically gravitate to incumbents. Mr. Lamont has received no contributions from political action committees, something his campaign boasts about. Instead, Mr. Lamont’s largest contributor is himself: He has already spent $2.5 million of his own money, and yesterday announced that he would personally match every dollar donated to his campaign over the Internet.

Anyone looking for evidence of Mr. Lieberman’s bipartisan appeal can find it in his roster of recent contributors, which includes organizations that traditionally give more to Republicans. They include engineering and construction firms, some with contracts in Iraq. Those firms include Bechtel, Fluor International and Siemens, which support Republicans 64 to 70 percent of the time, according to data compiled by PoliticalMoneyLine, which tracks campaign and lobbying activities.

Florida Power and Light, which supports Republicans 84 percent of the time, gave $5,000 to Mr. Lieberman. Areva Cogema, a builder of nuclear power plants that gives 70 percent of its contributions to Republicans, contributed $1,000.

An Ohio law firm that directs 80 percent of its donations to Republicans gave $1,000. SRA International, a technology consultant that favors Republicans 66 percent of the time, gave $1,000. America’s Health Insurance Plans, representing health insurers, gives to Republicans 71 percent of the time and donated $2,000 to Mr. Lieberman.

The reasons for their support differ, and are not always clear. Most of these contributors did not support Mr. Lieberman in 2000, and many have supported only Republican candidates in Connecticut; the only other Connecticut candidate to receive a contribution this year from Areva Cogema, for example, was Representative Nancy L. Johnson, a Republican.

Mr. Lieberman sits on the Armed Services Committee and so would be expected to draw contributions from defense firms. Also, his senior position on the Environment and Public Works Committee partly explains the donation from the contractors’ association, said Stephen E. Sandherr, the group’s chief executive, who added that other factors come into play when backing a candidate.

“We also look at where they are on tax policy, regulatory policy, being responsive to our members in our states,” Mr. Sandherr said. “He listens. He’s very responsive to our industry.”

The Ohio law firm, Vorys, Sater, Seymour and Pease, which supported both Mr. Lieberman, for re-election to his Senate seat, and George W. Bush in 2000, did not respond to a message yesterday. Neither did the Hardwood Federation, which represents the lumber industry and gives to Republicans about 80 percent of the time. That national group, whose president runs a hardwoods company in Connecticut, has contributed $7,500 to Mr. Lieberman.

“It doesn’t mean much to us,” said Sean Smith, Mr. Lieberman’s campaign manager. “If people give us money because they support us, that’s great. But Joe Lieberman is under no obligation to support them. We’re just trying to keep up with the money machine that Lamont is.”

Mr. Lieberman’s political action committee contributions were dwarfed by the donations he received from individuals, which accounted for just over $1 million between March and July.

He received $1,000 donations from former Clinton administration officials, including Samuel R. Berger, who was President Bill Clinton’s national security advisor, and Jamie S. Gorelick, a former deputy attorney general.

The most prominent names on Mr. Lamont’s donor list include several celebrities, including Rosie O’Donnell, Paul Newman (who lives in Westport, Conn.) and Norman Lear, the producer.

The campaigns of both Mr. Lamont and Mr. Lieberman have ballooned with donations from outside Connecticut, reflecting how the contest has become a national battleground for Democrats divided over Mr. Lieberman’s willingness to support the Bush administration on issues like the Iraq war.

With nearly 80 percent of his money coming from outside Connecticut, Mr. Lieberman had the highest rate of out-of-state money of any incumbent senator, according to the Center for Responsive Politics, which tracks political contributions. That figure does not include donations in the most recent campaign finance filing.

Mr. Lamont, too, has an increasingly high number of out-of-state contributors, who made up roughly 70 percent of his donations in the most recent filings, according to a list of donors provided by the campaign. Donations made through the Internet have made up nearly 64 percent of the $1.4 million in individual contributions that Mr. Lamont has raised since entering the race in March, according to his campaign’s figures.

As of last evening, the campaign had collected about $33,000 through its Web site and various blogs. Mr. Lamont’s campaign manager, Tom Swan, said he was confident the candidate’s supporters would be attracted to Mr. Lamont’s promise to match their money.

“The fact that Ned could fund thousands of dollars allows this campaign to do what 90 percent of others can’t, which is challenge an incumbent,” Mr. Swan said.

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